Girls, how do you act around really hot guys you're into when you have a boyfriend?

Let's say you know a really cute funny guy from class but you have a boyfriend, and you're into him but you have a boyfriend, how will you act around him and what sorts of things would you do if you're interested?

People, no matter who they are with, cannot control what they find attractive. Those two girls mysteriously lose all ability to find another man attractive when they are in a committed relationship. I CALL BS.

If they were honest, they would say that every now and then they may find another guy attractive (it's human nature). But, due to being committed to their boyfriend, they ignore it, stay away and do not act on it.

I find people good looking but I'm not sexually attracted to them. I wouldn't act upon them being good looking because there wouldn't be any feelings to act upon. Most I'd want to do is be friends with them.